A Mystery in Smoke
by Best Damn Avocado
Summary: Natasha's mysteries are Sherlock's to solve, and he takes great pleasure in the task. Sherlock Holmes and Natasha Romanoff, established relationship.


Natasha didn't move into Sherlock's flat overnight. She started small, wedging her books into his already packed bookshelves during her visits, wherever they fit. Mostly thick, heavy books with yellowed pages and cracked spines.

Always falling apart. Always in Russian.

Sherlock wondered at first why she didn't bother replacing them with new ones altogether. She certainly read them often enough that it justified the additional expense, and at any rate, she could afford it. Her copy of _War and Peace_ had been mended so many times the image on the cover was no longer even visible.

"Even the pages are falling out," he commented while he thumbed through it, carefully so as not to damage it further, though still thoroughly confused. "Why do you keep it? You realize there's no shortage of shops that carry new and superior copies only minutes away." A thin page came out in his hands. He stole a surreptitious glance to make sure Natasha wasn't looking, and covertly tucked it back into place. "We could go down and replace the lot of these this afternoon."

"I like my books the way they are." Natasha didn't lift her eyes from the screen of her laptop, reading with a furrowed brow. Something important, Sherlock deduced. She usually gave him her full attention when he spoke.

When she started typing, he closed the book with a soft snap. "Sentiment?"

She peeked at him, finally, and cracked a small, enigmatic smile. "You're the consulting detective," she teased. "You tell me."

"Minx," he accused, but he welcomed the mystery.

Natasha was called away for work the next day. Some political matter that wold keep her occupied for an unspecified amount of time, despite her many promises she'd be back within a week, at most.

Sherlock toyed with several theories in her absence. Whenever he could spare the time between cases he'd turn the matter over in his head, if nothing else, for the satisfaction of his unquenchable curiosity. Went as far as taking all her books from his shelves and going through each of them one by one, searching for a common thread.

A grand total of fifteen books in all, first editions, and only one thing to link them together once he'd inspected them close enough. The scent of smoke, just barely clinging to their pages. _All_ their pages.

A little experiment was in order.

John stared him down hard as they pushed their way into the lab at St. Bart's. " _Don't_ do this, she'll murder you."

"I'm not taking the whole thing apart, I just need a page," Sherlock said innocently.

"What are we doing? Wasn't expecting you today." Molly darted curious brown eyes between them, fiddling anxiously with the pen in her hands. Her paperwork was neatly stacked in front of her, barely touched.

"Testing for fire damage," Sherlock explained. Molly dropped her pen and hopped to work, eager for something to break the tedium of a slow day.

"You need a page for each book," John continued. "Fifteen pages in all, and not all of them can afford to lose a page, Sherlock. You're sure this is worth the risk of a… sting? Whatever she calls those."

"She knows my methods, must've known this was a possibility." Sherlock's tone was dismissive, but he didn't miss John pursing his lips in disapproval. Even without words to accompany the gesture, Sherlock knew what he was saying.

 _More than a bit not good, mate_.

Sherlock sighed, dropped the plastic bag full of papers on the surface in front of him, and tugged at his scarf. "I'll do as little damage as necessary," he grudgingly conceded. "Acceptable?"

"Right, well, I suppose that's the best we're going to get under the circumstances." John leaned against the bench, watching Molly as she hustled back in their direction with a smile on her face and extra gloves in her hand. "Just leave me out of it when you tell her what you've done, yeah?"

"Your complicity in this matter will forever remain a secret, you have my word." Sherlock nodded tersely, then waved him away. "Now go away, I'm busy."

All fifteen books turned up the same results in the end. Sherlock had been right from the beginning. Sentiment had driven Natasha to keep them, find them in the first place, though not quite the way he'd been expecting.

And now he knew exactly what he needed to do.

He got to work as soon as he left St. Bart's, gathering all of Natasha's books, and delivering them to a specialist in book restoration and repair. She came highly recommended by Mycroft himself. John protested, yet again, pointing out that Natasha might not want her books restored at all. Sentiment could be powerful that way.

Sherlock dismissed the advice. John's intentions were noble, downright admirable, but Sherlock always knew better where Natasha was concerned. Her heart was _his_ puzzle to solve, and he took great pleasure in the task.

By the time she arrived from the States, he had her books rebound, and the missing pages restored. He tucked them back into his bookshelves, carefully and exactly where she'd put them when she'd first brought them over.

Natasha noticed within seconds of stepping inside the living room, tired but smiling after a long trip. She'd been halfway to kissing him when she'd stopped, suddenly, and walked past him towards his shelves. "You've been busy."

"You know I never can resist a mystery."

Sherlock took the bag from her hand and followed her over, nervously studying her face as she touched one of the spines. Her fingertips grazed the leather hesitantly, almost reverently, he silently mused. When she finally turned her eyes his way, they were wet and rimmed with pink.

His shoulders sagged in defeat. "I did it wrong," he concluded.

Natasha pounced before he had a chance to register she'd moved. She was all warm, soft lips and strong arms wrapping around his neck in a possessive grip he knew all too well. He stumbled back, dropping her bag only to reach for her and pull her close.

She always fit so well against him.

She broke the kiss too soon. "You did it right," she breathed. "You did it _exactly_ right. What gave it away?"

"Fire damage, all of them." Sherlock gave his brain a hard nudge to get it working again. "You've always been eminently practical, you would've replaced those books long ago if there was nothing special about these particular copies. Once I detected the fire damage in all of them, not just a few, it was fairly easy to deduce the reason. They belonged to your parents."

Natasha stared at him in what might've been wonder, or something close to it. He couldn't tell with their faces so close. "Only a few of them survived the fire," she explained. "A friend of theirs kept them, and when I visited her a couple of years ago, after the mess with S.H.I.E.L.D. when I was searching for my parents, I explained who I was." She smiled a little. "And she gave them to me. Thank you for restoring them." Her eyes strayed back to the books, but only briefly. "I meant to do it myself, when I finally found a place. A real place, not just a safe house, or bolthole, or…"

Sherlock drew her in for another kiss, soft and so much tenderer than the first. " _Any time, Natalia_."

He didn't miss the meaning behind her words.


End file.
